#include <stdio.h>

int add(int a, int b);
int subtract(int a, int b);
int multiply(int a, int b);
int divide(int a, int b);

int main() {
    int num1 = 20, num2 = 5;
    char operation = '*';  // 支持 +, -, *, /
    int result;

    if (operation == '+') {
        result = add(num1, num2);
    } else if (operation == '-') {
        result = subtract(num1, num2);
    } else if (operation == '*') {
        result = multiply(num1, num2);
    } else if (operation == '/') {
        if (num2 == 0) {
            printf("Error: Division by zero!\n");
            return 1;
        } else {
            result = divide(num1, num2);
        }
    } else {
        printf("Error: Invalid operation!\n");
        return 1;
    }

    printf("Result: %d\n", result);

    switch (result) {
        case 0 ... 10:
            printf("The result is between 0 and 10.\n");
            break;
        case 11 ... 100:
            printf("The result is between 11 and 100.\n");
            break;
        default:
            if (result > 100) {
                printf("The result is greater than 100.\n");
            } else {
                printf("The result is less than 0.\n");
            }
            break;
    }

    return 0;
}

int add(int a, int b) {
    return a + b;
}

int subtract(int a, int b) {
    return a - b;
}

int multiply(int a, int b) {
    return a * b;
}

int divide(int a, int b) {
    return a / b;
}
